1. Field of the Invention
The present invention generally relates to positive-displacement-type refrigerant compressors including reciprocating type refrigerant compressors and rotary type refrigerant compressors. More particularly, the present invention relates to an oil-separating and lubricating system incorporated in a positive-displacement-type refrigerant compressor for the lubrication of various internal portions and movable elements of the positive-displacement-type refrigerant compressor by separating oil from a refrigerant at a high pressure and by supplying the separated oil to the portions and elements to be lubricated.
2. Description of the Related Art
In a positive-displacement-type refrigerant compressor mainly incorporated in a vehicle climate control system, lubrication of various internal portions and movable elements of the compressor is achieved by an oil, i.e., an oil mist suspended in a gas-phase refrigerant which is compressed within the compressor. Therefore, when the compressed refrigerant containing and suspending therein the oil is delivered from the compressor to an external refrigerating system in the climate control system, the oil is attached to an internal wall of an evaporator of the refrigerating system to result in a reduction in the heat exchanging efficiency of the evaporator. Thus, in the conventional refrigerating system, an oil separating unit is arranged in a high pressure gas pipe extending from the refrigerant outlet of the compressor to a condenser, and the separated oil is returned from the oil separating unit into the interior of the refrigerant compressor via a separate oil-return conduit. However, an arrangement of the oil separating unit in the gas pipe and an addition of the oil-return conduit to the refrigerating system make it cumbersome to assemble the refrigerating system of the vehicle climate control in the rather narrow assembling space in a vehicle. Further, the oil-return conduit is usually formed by a long pipe element having a small diameter, and accordingly, clogging easily occurs during the operation of the compressor. Therefore, a refrigerant compressor has been provided which is provided with an oil-separating unit directly incorporated therein.
The oil-separating unit incorporated in the conventional refrigerant compressor is provided with an oil storing chamber formed in the compressor for storing an oil separated from a refrigerant in a high pressure region within the compressor, and an oil-return passage communicating the oil storing chamber with a low pressure region such as a crank chamber in the compressor for supplying the oil from the oil storing chamber to the low pressure region. The oil-return passage is provided with a valve unit arranged therein to control an amount of oil to be supplied into the low-pressure region in response to a change in the operating condition of the compressor.
For example, Japanese Unexamined Patent Publication (Kokai) No. 9-324758 (JP-A-9-324758) discloses a valve unit which functions to interrupt the oil-return passage during the running of the compressor, and to permit the oil to flow therethrough when the operation of the compressor is stopped.
Japanese Unexamined Patent Publication (Kokai) No. 6-249146 (JP-A-6-249146) discloses a valve unit used in a variable displacement type refrigerant compressor and operates in such a manner that when an oil separating chamber is kept at a high pressure during a large displacement operation of the compressor, a restricted amount of oil is permitted to pass through an oil-return passage via the valve unit, and when the oil separating chamber is kept at a low pressure during a small displacement operation of the compressor, a large amount of oil is permitted to pass through the oil-return passage via the valve unit.
Nevertheless, in the two conventional incorporated type oil separating systems of JP-A-9-324758 and JP-A-6-249146, no positive means to completely prevent the oil from being delivered from the interior of the compressor into an associated refrigerating system is provided. Namely, since the lubrication of various internal portions and movable elements of the refrigerant compressor must rely on mainly the oil suspended in the refrigerant returned from an external refrigerating system, at least when the refrigerant compressor is stopped, an amount of the oil supplied to the low pressure region in the compressor must be increased to prevent lack of lubricant at the start of operation of the refrigerant compressor. In this connection, even if the amount of oil delivered from the refrigerant compressor is small, delivery of the oil from the compressor into the external refrigerating system results in preventing an increase in the heat exchanging efficiency in the refrigerating system depending on the amount of oil in a unit weight of refrigerant.
Moreover, when the compressor is stopped, and if a large amount of oil is supplied to the low pressure region in the compressor, the oil remaining in the low pressure region is suddenly agitated due to the restarting of the compressor, and will cause the splashing of the oil. Accordingly, compression of the oil, i.e., a liquid or oil compression occurs within the respective cylinder bores. Thus, an unpleasantly strong shock and a noise are generated in the interior of the refrigerant compressor.